For the discretized problem related to (REF ), in [1]} the following spaces are defined for a triangulation \(T_h\)  of the domain \(\Omega \)  and a fixed integer \(k\ge 0\) ,
\(\begin{split}&H_h^k:=\lbrace \mathbf {v_h}\in H(\mbox{div};\Omega )\ |\ \mathbf {v_h}|_K\in RT_k(K)\text{ for all }K\in T_h\rbrace ,\text{ and}\\&L_h^k:=\lbrace w_h\in L^2(\Omega )\ |\ w_h|_K\in \mathbb {P}_k(K)\text{ for all }K\in T_h\rbrace ,\end{split}\) 
